This invention is concerned with ion implanters and particularly ion implanters intended for processing single wafers one after the other. In particular, the invention is concerned with the handling of such single wafers in the process chamber of the implanter in which implantation takes place.
Ion implanters for processing single wafers one after the other are known from for example U.S. Pat. No. 5,229,615. In such single wafer ion implanters, a crucial part of the process is the handling of the wafer in the process chamber, both the way in which the wafer is mechanically scanned for processing, and the way in which a processed wafer is removed from the chamber and a fresh wafer is supplied to the chamber. Usually, during implantation, the wafer is held on a chuck. In many applications, the ion beam used for implantation has a beam cross-section which is much smaller than the area of the wafer and so coverage over the entire wafer surface is ensured by mutually scanning the ion beam and the wafer during processing. For single wafer implanters, it is known for the beam itself to be scanned in one direction across the wafer, e.g. by electrostatic or electromagnetic means, and for the wafer to be mechanically scanned in a direction generally orthogonal to the plane of scanning of the beam. To achieve this mechanical scanning, the chuck carrying the wafer during processing is itself moved to and fro through the plane of the scanned beam.
Commonly, the beam is scanned in a horizontal plane so that the mechanical movement of the chuck carrying the wafer is generally vertical. The above referred U.S. Pat. No. 5,229,615 achieves the vertical scanning of the chuck and wafer by means of a mechanism supporting the chuck from a position horizontally spaced from the scanned beam.
It is also desirable to enable the angle presented by the wafer on the chuck to the scanned beam to be adjustable. This permits the angle of implantation into the wafer to be adjusted. Relatively high implant angles may be desirable, especially for implantation into the sides or walls of trenches, troughs or mesas on a previously processed wafer. It is considered desirable for the mechanism which provides the mechanical scanning action of the chuck and wafer to move the wafer through the beam always along a line in the plane of the wafer, irrespective of the angle of tilt of the wafer for the purpose of providing an angled implant. Such an arrangement is provided, for example, by WO 99/13488.
Mechanisms which support the wafer and chuck for mechanical scanning from one side of the beam (at a horizontally spaced position relative to the beam, assuming the beam is itself scanned in a horizontal plane) can more readily provide the desirable mechanical scanning action of the wafer, always in the plane of the wafer, as the wafer is tilted to different implant angles. In the case of U.S. Pat. No. 5,229,615 and WO 99/13488, this scanning action is provided by mounting a linear scanning mechanism on a structure which can as a whole be rotated about an axis generally parallel to the plane of the scanned beam and through the plane of the wafer. Then, adjustment of the rotary position of the scanning mechanism about this axis tilts the wafer to desired implant angle and also ensures subsequent mechanical scanning of the wafer is then along a line in the plane of the wafer at the new tilt angle.
It is also highly desirable for the chuck supporting the wafer during scanning to be orientated in a generally horizontal position for unloading a processed wafer and loading a new wafer. Then a new wafer can be initially supported on the chuck by the action of gravity. It will be understood that wafer handling within the process chamber is typically performed by means of a robot arm which can place a wafer over a horizontally orientated chuck and then release it, and conversely grip a processed wafer on a chuck and then remove it.
In each of U.S. Pat. No. 5,229,615 and WO 99/13488, the chuck can be rendered horizontal by rotating the tilt mechanism of the mechanical scanning arrangement through 90xc2x0. In this position, the chuck and wafer holder is invariably in the plane of the scanned beam and so the beam is interrupted for loading and unloading.
U.S. Pat. No. 5,003,183 discloses a further single wafer scanning arrangement in which the wafer holder is brought to a horizontal orientation for loading and unloading, in a position in the plane of the scanned beam, but to one side clear of the beam path. In this way loading and unloading can proceed without interrupting the beam, so that a second scanning mechanism may then be included to implant a second wafer while the first wafer is being removed or replaced. This allows almost continuous implanting without interruptions for loading and unloading. However, because the loading/unloading positions are to the side of the scanned beam, the process chamber must be relatively wide. Also separate wafer handling stations are required for the scanning mechanisms on opposite sides of the beam.
It is an objective of the present invention to provide a single wafer ion implanter in which loading and unloading of the wafer holder can be preferred out of the line of the ion beam.
The present invention provides, in one aspect, an ion implanter for serially processing single wafers comprising a vacuum chamber, a substrate holder in the vacuum chamber, an ion beam generator for generating abeam of ions to be implanted, a beam scanner for scanning the beam in a horizontal plane across a target substrate on the holder, and a scanning mechanism comprising an arm having an inner end carrying the substrate holder and an arm actuator horizontally spaced from the scanned beam, said scanning mechanism being operative to scan the substrate holder in a generally vertical direction through the plane of the beam for implantation of a wafer, and having a loading and unloading position in which the substrate holder supports a substrate in a substantially horizontal orientation at a position above the plane of the beam.
In an implanter according to the present invention it is preferred that the substrate holder is mounted for rotation about a first axis to move between the loading and unloading position and a position in which a substrate provided thereon is located in the path of the beam, the substrate holder being mounted for rotation about the first axis to locate the substrate in the path of the beam upstream of the first axis.
In an implanter according to the present invention the scanning mechanism may further comprise a rotatable hub on which the arm is rotatably mounted, the arm being mounted on the hub for rotation about the second axis, and the hub being mounted for rotation about the first axis which is normal or substantially so to the second axis. The arm is preferably movable in a plane which is parallel to and spaced from the second axis and preferably forwardly of the second axis, so that, as the hub is rotated about its first axis to carry the substrate holder out of the path of the ion beam, the rotation thereof causes the substrate holder to be moved above the plane of the beam as desired. The first and second axes may be coplanar.
The hub may be mounted at least partially within the wall of the vacuum chamber in airtight relationship therewith.
In an ion implanter according to the present invention, two substrate holders, each mounted on a respective scanning mechanism, may be arranged in face to face relationship such that each substrate holder can be moved between the loading and unloading position as aforesaid and a second position in which a substrate located on a respective substrate holder can be scanned in the generally vertical direction through the plane of the beam. Each arm may be movable to move the substrate holder to the same loading and unloading position such that, while one substrate holder is in that position, the second substrate holder is being scanned through the plane of the beam, and the positions of the two substrate holders can be interchanged without coming into contact with one another. Preferably, the two hubs are coaxially mounted.
The, or each, hub may be rotatable about its axis of rotation so that the, or each, substrate holder can be presented at a tilt angle to a beam of ions directed at a substrate mounted on the substrate holder. Preferably the, or each, arm is rotatable about its axis of rotation so that the, or each, substrate holder can be swept at its respective tilt angle through the beam of ions. The, or each, substrate holder can be controllably rotated through any angle about its axis of rotation while at a selected respective tilt angle.
In an implanter according to the present invention, the, or each, hub may provide a mounting platform which is spaced from and parallel to the axis of rotation of the hub and the respective arm is mounted for rotation thereon about its axis of rotation. The, or each, hub may be mounted in the wall of the vacuum chamber for rotation about its axis and in airtight relationship with the wall of the vacuum chamber.
The present invention further provides an ion implanter comprising a vacuum chamber, first and second substrate holder assemblies mounted in the vacuum chamber, an ion beam generator for directing a beam of ions at a substrate target when presented in the path of the beam, and each substrate holder assembly comprising a substrate holder and an arm associated with each substrate holder and mounted for movement in the vacuum chamber to move a first one of the substrate holders between a first position in which the substrate holder is positioned in the path of the beam to permit ion implantation in a target substrate mounted on that substrate holder and a second position in which the substrate holder is positioned for loading or removal of a target substrate from the substrate holder while the second one of the substrate holders is being moved in the opposite direction between the first position and the second position.
The second position is preferably located above the path of the beam.
The first and second substrate holder assemblies are preferably mounted in face to face relationship within the vacuum chamber.
Preferably each arm is mounted on a respective rotatable hub and the axes of rotation of the two hubs are co-linear, each arm being mounted for rotation on its respective hub in a manner such that it can be moved, when a substrate holder is being moved between its first position and its second position, and will not obstruct the movement in the opposite direction of the other substrate holder.
The present invention further provides an ion implanter comprising a vacuum chamber, a substrate holder in the vacuum chamber, an ion beam generator for directing a beam of ions at a substrate target mounted on the substrate holder, and a hub located in the wall of the vacuum chamber and rotatable about a first axis in the path of the beam, an arm mounted on the hub for rotation about a second axis normal to the first axis and the substrate holder being mounted on the arm for rotation about a third axis normal to the first axis, the construction and arrangement of the assembly of the substrate holder, the arm and the hub permitting movement of the substrate holder between a first position in which the substrate holder can be positioned in the path of the beam at any desired angle of tilt to the path and forward of the third axis, and a second position in which the substrate holder is positioned above the beam for loading or removal of a target substrate from the substrate holder. Loading or removal of a target substrate at a position above the beam enables the implanter to continue to operate without the necessity to shut off the beam or interpose a shutter between the beam and the target substrate.
There now follows a detailed description of an ion implanter according to the present invention which has been selected for description to illustrate the invention by way of example only and not by way of limitation.